The present invention relates to a mask feed method and apparatus for exposure replicate systems and more particularly to a mask feed method and apparatus for feeding and highly accurately setting an integrated circuit pattern printing mask in a proximity exposure replicate system for printing integrated circuit patterns on a semiconductor wafer for the manufacture of a VLSI (very large-scale integrated) circuit.
In a known type of proximity exposure system employing soft X-rays, a mask containing a circuit pattern to be printed is positioned opposite at such a very close distance as 100 .mu.m or less to a semiconductor wafer to be exposed and the exposure is made. As a result, structurally the gap between a mask holder for holding the mask and a wafer stage for carrying the wafer thereon is very small so that the mask must be set in this very small gap and therefore it is not an easy matter to change the masks upon change of the patterns to be printed.
An example of the proposals heretofore made to overcome the foregoing mask changing difficulty is a method disclosed in Japanese Patent Publication No. 56-49449 in which a mask holder is separated from a mask stage at an exposure position and the mask holder having a mask mounted thereon at a position different from the exposure position is moved into the exposure position, thereby effecting the desired alignment and transfer of the mask onto the mask stage. However, this method still involves difficult problems to be solved in that not only an additional mechanism is required for moving the mask holder but also specially a large space for movement is required, the use of these moving parts involves instability factors in the stopping accuracy of the mask during the exposure and so on.
Then, in the case of the proximity exposure system of the step-and-repeat type, the range of movement of the wafer stage is large from the first and therefore it is conceivable to effect the mask movement of the above-mentioned method by means of the wafer stage. In this case, what is to be noted is the fact that generally the traveling speed of the wafer stage must be increased as far as possible so as to increase the processing rate of the exposure replicate system and that the occurrence of any shift in the position of the mask mounted on the wafer stage during its high-speed movement causes an inconvenience during, for example, the transfer operation of the mask. While the mask may be fixedly mounted on the wafer stage by means of the vacuum chucking means for wafer chucking purposes, not only are the mask and the wafer not the same in shape but also the mask must be chucked without allowing anything to come into contact with the inner circuit pattern portion of its back excluding the peripheral portion, in contrast to the wafer which is chucked over all its back side as far as possible so as to improve its surface flatness. Particularly, in the case of a mask for soft X-ray exposure purposes, the X-ray penetrating portions of the pattern are as thin as about 1 to 10 .mu.m and weak and therefore there is the danger of these portions being broken by the vacuum chucking. While this deficiency can be overcome by chucking a mask-carrying jig on the wafer chucking means of the wafer stage, mounting the mask on the jig and moving the mask, each time the mask changing is effected the mask-carrying jig must be mounted and demounted in the proper position and posture with respect to the wafer chucking means and this inevitably causes such deficiencies as deterioration of the operating efficiency and limitation of the processing capacity of the system.